Method and System for Detecting Changes in a Network Using Simple Network Management Protocol Polling

ABSTRACT

In an embodiment, methods and systems have been provided for detecting changes in a network using improved Simple Network Management Protocol (SNMP) polling that reduces network traffic. Examples of changes in the network include, but are not limited to, configuration and behavioral changes in a network device, and response of network device to a network change. A Network Management Station (NMS) periodically polls Management Information Base (MIB) groups instead of periodically polling individual MIB object instances. The NMS receives the Aggregate Change Identifiers (ACIs) of MIB groups in response to polling, from a SNMP agent. The changes in the received ACIs represent the changes in the MIB groups. A change in an MIB group represents changes in the MIB object instances of the MIB group. The ACIs can be checksum, timestamp, and a combination of number of MIB object instances in a group and checksum of the MIB group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority to U.S. application Ser. No. 11/440,325, filed on May 23, 2006, the entire contents of which are herein incorporated by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate, in general, to network management. More specifically, embodiments of the present invention relate to methods and systems for monitoring Management Information Base (MIB) for use with network management protocols.

2. Description of the Background Art

A Network Management Station (NMS) monitors and administers network devices in a network using application layer protocols such as a Simple Network Management Protocol (SNMP). The NMS gathers information about the changes in the network devices to monitor and administer the network devices. The information about the changes such as configuration and behavioral changes in a network device, and response of network devices to a network change, constitute management information of the network devices. A software module such as an SNMP agent running on the network device provides management information of the network device to the NMS using Management Information Bases (MIBs). The MIBs are present in the network device. An MIB includes a large number of variables known as MIB objects. The NMS monitors the network devices by monitoring the changes in the MIB objects. The changes in the MIB objects lead to changes in the network devices and consequently, the changes in the network.

According to conventional methods, the NMS may use asynchronous and synchronous monitoring mechanisms, to monitor the changes in the MIB objects. One such example of asynchronous monitoring is an SNMP-trap mechanism. In the SNMP-trap mechanism, the network device sends SNMP traps to the NMS if the MIB objects are changed. However, it is possible that in some cases, the SNMP traps are not received by the NMS. As a result, the SNMP-trap mechanism is not completely reliable. Further, the SNMP-trap mechanism is applicable when a trap for a change in the MIB object is defined at the time of defining the MIB object. Moreover, the SNMP trap-mechanisms require highly available NMS.

In another asynchronous monitoring mechanism, the NMS may use Remote Monitoring (RMON) to monitor the changes in the MIB objects. However, the RMON uses a large memory of the network devices for monitoring the MIB objects. As a result, the RMON is not suitable for monitoring a huge list of the MIB objects.

In another conventional method, the NMS may use SNMP polling as a synchronous monitoring mechanism for monitoring the changes in the MIB objects. In SNMP polling, the NMS periodically polls the MIB objects. The periodic polling of each MIB object results in detecting changes in the MIB objects that have occurred between two subsequent time-periods. SNMP polling is more reliable in comparison to asynchronous mechanisms. Moreover, SNMP polling does not require highly-available NMS. However, the SNMP polling of each MIB object generates a large amount of SNMP traffic in the network. Moreover, the SNMP polling of each MIB object is not useful when no changes are detected in the MIB objects. As a result, the method of SNMP polling of each MIB object has to be optimized to avoid the generation of a large amount of traffic in the network.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an environment, wherein embodiments of the present invention can be performed.

FIG. 2 illustrates a network device and a Network Management Station (NMS) in accordance with an embodiment of the present invention.

FIG. 3 illustrates MIB groups in accordance with an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a method for polling an MIB group in accordance with an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a method for detecting a changed MIB group in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention provide methods, systems, and computer-readable media for detecting changes in a network using improved Simple Network Management Protocol (SNMP) polling that reduces the network traffic. In the description herein for embodiments of the present invention, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the present invention.

Embodiments of the present invention provide a method and system for detecting changes in a network using improved Simple Network Management Protocol (SNMP) polling that reduces network traffic. In operation, Network Management Station (NMS) periodically polls Management Information Base (MIB), which is a collection of management information about network devices. The MIB includes a large number of variables known as MIB objects. Changes in the MIB objects indicate the occurrence of changes in the network devices. An SNMP agent provides management information of a network device in the form of changes in the MIB objects. The NMS monitors the changes in the network devices by monitoring the changes in the MIB objects. The changes in the network devices lead to changes in the network.

In an embodiment of the present invention, the NMS monitors Aggregate Change Identifiers (ACIs) of a group of MIB object instances instead of monitoring each of the MIB object instances. A change in an ACI of an MIB group of the MIB object instances indicates a change in at least one MIB object instance of the MIB group. As a result, the NMS polls only those MIB object instances for which a change is detected in the ACI of their MIB group. If no change is detected in an ACI of an MIB group, then the MIB object instances of the MIB group are not polled. As a result, there is a decrease in the number of the MIB object instances polled by the NMS to detect the changes in the network. Moreover, the traffic generated in the network can be quite reduced. At the SNMP agent, there is a huge reduction in the number of SNMP packets that are constructed and processed during the polling of each of the MIB object instances present in the network. Further, the time taken by the NMS to detect the changes in the network is also reduced.

Referring now to drawings, more particularly by their reference numbers, FIG. 1 illustrates an environment, wherein embodiments of the present invention can be performed. The environment includes a network 100. Network 100 includes network devices 102 a, 102 b, 102 c, 102 d, and 102 e, hereinafter collectively referred to as network devices 102. Network 100 further includes a Network Management Station (NMS) 104. NMS 104 is a system for monitoring and administering network devices 102 in network 100. NMS 104 updates itself by continuously monitoring the changes taking place in network devices 102. Examples of network devices 102 include, but are not limited to, gateways, routers, firewalls, repeaters, bridges, and switches. Network devices 102 can be connected in various network topologies such as ring, tree, star, bus, mesh, and so forth.

In accordance with an embodiment of the present invention, NMS 104 monitors network 100 by periodically polling management information of network devices 102. Management information includes information related to changes in network devices 102. The changes can be due to the static changes in network 100 or the changes in the operational environment of network 100. Accordingly, the changes in network devices 102 lead to changes in the way traffic is transported across network 100. Examples of changes in network devices 102 include, but are not limited to, configuration or behavioral changes in network devices 102, and response of network devices 102 to a change in the configuration of network 100. The behavioral change of network devices 102 can be, for example, a new entry in the routing table of network devices 102. Further, the response of network devices 102 to a change in network 100 can be due to, for example a link partner such as a network device 102 a at the other end of a wire or across a portion of network 100 going down during an auto-negotiation, to detect the various modes that exist in network device 102 b on the other end of the wire. Each link partner advertises it own abilities to automatically configure the highest performance mode of interoperation. For example, network devices 102 a and 102 b may be link partners. If one of the link partners malfunction, network operational parameters can degrade as traffic may be routed along other paths.

Moreover, NMS 104 can also detect the changes in network devices 102 that are related, but not limited to Virtual Large Area Networks (VLANs), port-to-VLANs association, spanning-tree states, channel states, and interface operational states. Further, the management information of network devices 102 is included in Management Information Bases (MIBs). A MIB includes a large number of variables known as MIB objects. The changes in the MIB objects may or may not represent the changes in network devices 102. For example, changes in MIB objects like traffic counters may not represent changes in network devices 102.

FIG. 2 illustrates a representative network device, such as network device 102 a and NMS 104, in accordance with an embodiment of the present invention. Network device 102 a includes a Simple Network Management Protocol (SNMP) agent 202 and MIB object instances 204 a, 204 b, 204 c, and 204 d, hereinafter collectively referred to as MIB object instances 204. MIB object instances 204 are a collection of management information about network device 102 a. The definition for the management information has been explained earlier. The changes in MIB object instances 204 indicate the changes in network device 102 a.

Accordingly, if NMS 104 is interested in detecting changes in network device 102 a, then NMS 104 sends requests to SNMP agent 202 for detecting changes in MIB object instances 204. SNMP agent 202 is a process running on network device 102 a that interfaces with MIB object instances 204. Further, SNMP Agent 202 is an application that performs the operational role of receiving requests from NMS 104. SNMP agent 202 receives the requests, processes the requests, and sends responses to NMS 104 in form of SNMP packets. The responses may include information about the value of MIB object instances 204. Further, the process of sending requests to SNMP agent 202 and receiving responses from SNMP agent 202 is hereinafter, collectively referred to as polling. In an embodiment of the present invention, NMS 104 is also referred to as an SNMP manager.

For example, NMS 104 may poll 100s of MIB object instances 204 present on each of thousands of network devices 102, in order to detect the changes in network 100. However, polling each of MIB object instances 204 present in network 100 results in generation of large amount of SNMP traffic in network 100. Moreover, NMS 104 takes large amount of time in polling each of MIB object instances 204 in order to detect the changes in network 100.

To reduce the polling of each of MIB object instances 204 in network 100, MIB object instances 204 are grouped together to form at least one MIB group. NMS 104 poll an MIB group. In response to a poll request of the MIB group, SNMP agent 202 sends an Aggregate Change Identifier (ACI) of the MIB group to NMS 104. NMS 104 checks for a change in the received ACI. The change in the received ACIs indicates a change in the MIB group. MIB object instances 204 of the MIB group can be further polled to detect the changes in network devices 102.

FIG. 3 illustrates MIB groups in accordance with an embodiment of the present invention. MIB object instances 204 are grouped together to form MIB groups 302 a and 302 b, hereinafter collectively referred to as MIB groups 302. MIB group 302 a includes MIB object instances 204 a and 204 b. Similarly, MIB group 302 b includes MIB object instances 204 c and 204 d. MIB object instances 204 are grouped on the basis of MIB definition. The MIB definitions are object group definitions that list MIB object instances 204 present in MIB groups 302. For example, the MIB definition defines or list down MIB object instances 204 a and 204 b for MIB group 302 a.

In an embodiment of the present invention, MIB groups 302 may also be grouped to form MIB groups 304. For the purpose of illustration, only two such MIB groups 304 a and 304 b are shown. Also, MIB group 304 b may include MIB groups 302. However, for the purpose of illustration, MIB groups 302 of MIB group 302 b are not shown. Similarly, MIB group 304 a can include a large number of MIB groups 302. For the purpose of illustration, only two such MIB groups 302 are shown. Further, each MIB group from MIB groups 302 may include more or fewer than the two illustrated MIB object instances 204.

However, the formation of MIB groups 304 is possible, but is not essential to carry out all the embodiments of the present invention. Similarly, MIB group 304 a can be grouped with other MIB group 304 b to form a higher level of grouping. The formation of groups within groups depends on the implementation of the various embodiments of the present invention. As a result, MIB object instances 204 and MIB groups 302 and 304 may form a multi-level hierarchy of MIB object instances 204. In network device 102 a, SNMP agent 202 interfaces with MIB object instances 204 and MIB groups 302 and 304. As a result, SNMP agent 202 can poll each of MIB object instances 204 as well as MIB groups 302 and 304.

In an embodiment of the present invention, an MIB group such as MIB group 302 a is formed by grouping MIB object instances 204 that do not change under the normal operation of network device 102 a. For example, MIB object instances 204 such as timers and counters that change due to traffic flow are preferably not grouped as they often change during the normal operation of network device 102 a. Moreover, the changes in MIB object instances 204, that are time or traffic dependent does not account to the changes NMS 104 is looking for. However, MIB object instance 204 a is a right candidate for grouping if at least one change in MIB object instance 204 a is due to a configuration or behavioral change in network device 102 a, or if the response of network device 102 a is due to a change in network 100.

MIB object instance 204 a is the right candidate for grouping if at least one of the changes in MIB object instance 204 a does not wholly depend on time. At least one of the changes in MIB object instance 204 a must indicate a configuration change of network device 102 a, a behavioral change in network device 102 a such as a new entry in a routing table or response of network device 102 a to a change in network 100. To illustrate, consider the change in MIB object instance ‘dot1dStpPortState’ that is defined in RFC 1493-MIB, the disclosure of which is incorporated herein by reference. Although the transition from a ‘listening’ to ‘forwarding’ state is solely dependent on time, the transition from ‘forwarding’ to any other state is dependent upon topology changes in network 100. As one change in MIB object instance is not time dependent, this MIB object instance is the right candidate for grouping and can be grouped.

In another embodiment of the present invention, a user can also define MIB groups 302 and 304. For example, in one embodiment, editable table rows are provided for network administrators to define MIB groups 302 and 304. The formation of MIB group 304 from MIB groups 302 should also comply with grouping conditions that are explained above.

In an embodiment of the present invention, NMS 104 periodically polls MIB group 302 a instead of periodically polling each of MIB object instances 204. SNMP agent 202 can compute an ACI of MIB group 302 a in response to the poll request of MIB group 302 a by NMS 104. Examples of the ACIs may include a checksum of MIB group 302 a, a timestamp of MIB group 302 a, and a combination of the number of MIB object instances 204 and checksum of the corresponding MIB group 302 a. An ACI can be a 32 or 64 byte word in memory associated with MIB group 302 a. However, the length of an ACI byte word may vary according to the implementation of the various embodiments of the present invention.

An example of textual convention for an ACI is provided below to illustrate the ACI:

--Textual conventions

AggregateChangeIdentifier::=TEXTUAL-CONVENTION

STATUS current

DESCRIPTION

-   -   “Aggregate change identifier for the set of objects mentioned as         part of the objects clause. The change identifier can either be     -   a) time stamp indicating the last change of any of the instances         of the set of objects as mentioned in objects clause     -   b) checksum computed on the set of objects as mentioned in the         objects clause     -   c) a combination of number of objects and checksum on the set of         objects as mentioned in objects clause.     -   The checksum algorithms if used can be standard based or         proprietary but the same algorithm needs to be used consistently         across device reboots so that the checksum computation is         consistent.”

SYNTAX OCTET STRING

A change in the ACI of MIB group 302 a indicates a change in at least one of MIB object instances 204 of MIB group 302 a. It will be appreciated that further polling of MIB object instances 204 may be required or desired when a change is detected in the ACI of MIB group 302 a.

In an embodiment of the present invention, NMS 104 polls MIB group 304 a. A change in the ACI of MIB group 304 a indicates a change in at least one of MIB groups 302. As a result, NMS 104 polls MIB groups 302 to detect the changed MIB groups 302. If a change is detected in the ACI of MIB group 302 a, then NMS 104 polls MIB object instances 204 of MIB group 302 a. For example, if 10,000 MIB object instances 204 are grouped to form 100 MIB groups 302, then 100 MIB groups 302 can be further grouped in 10 MIB groups 304. If NMS 104 is interested in detecting the changes in each of 10,000 MIB object instances 204, then NMS 104 can start polling MIB groups from the highest level of multi-level hierarchy and can come down to polling of few MIB object instances 204. As a result, the concept of multi-level hierarchy helps in localizing the changed MIB object instances 204 easily.

The method of periodically polling an MIB group such as MIB group 302 a is explained in detail in conjunction with FIG. 4.

FIG. 4 is a flowchart illustrating a method for periodically polling MIB group 302 a in accordance with an embodiment of the present invention. At 402, NMS 104 polls MIB group 302 a in order to detect changes in MIB group 302 a. At 404, SNMP agent 202 receives the request for detecting changes in MIB group 302 a. At 406, SNMP agent 202 computes an ACI of MIB group 302 a. At 408, SNMP agent 202 sends the computed ACI of MIB group 302 a to NMS 104 in form of SNMP packets. At 410, NMS 104 stores the received ACI. NMS 104 processes the SNMP packets in order to detect the changes in the received ACI. The received ACI persists at NMS 104 until the next polling of MIB group 302 a occurs.

In accordance with an embodiment of the present invention, SNMP agent 202 computes the ACI of MIB group 302 a, each time it receives a poll request for MIB group 302 a. However, if no changes have occurred in MIB object instance 302 a, then the ACI of MIB group 302 a also remains unchanged. As a result, SNMP agent 202 can send an ACI computed in a previous polling to NMS 104 in response to a poll request for MIB group 302 a. However, if MIB group 302 a is changed since previous polling, then SNMP agent 202 again computes the ACI of MIB group 302 a. Moreover, SNMP agent 202 computes the ACI of MIB group 302 a only when it receives the poll request for MIB group 302 a.

In an embodiment of the present invention, an incremental checksum is an aggregation technique that is primarily applicable to large sets of MIB groups where computation of an ACI such as checksum in response to a small change in network device 102 a is expensive. For example, consider a configuration change taking place in network device 102 a. The configuration in totality may be represented by 1000 MIB groups 302 that are part of a MIB group such as MIB group 304 a. Therefore, SNMP agent 202 computes the checksum of 1000 MIB groups 302 when it receives the poll request for MIB group 304 a. However, if the configuration change has resulted in a change in only a 10^(th) MIB group such as MIB group 302 a, then there is no need to re-compute the checksum of all 1000 MIB groups 302. The checksum is computed incrementally only for MIB group 302 a on the basis of a checksum computed for MIB group 302 a in a previous polling. MIB group 302 a is marked as ‘dirty’ as a change has occurred in MIB group 302 a. SNMP agent 202 computes the incremental checksum for ‘dirty’ MIB group 302 a with reference to an already computed checksum in a previous polling of MIB group 302 a. Also, an already computed checksum of MIB group 302 a is marked as ‘invalid’ if some part of the memory of MIB group 302 a is marked as ‘dirty’. The already computed checksum that is marked as ‘invalid’ is then used to compute the incremental checksum of MIB group 302 a in a subsequent polling. SNMP agent 202 computes the incremental checksum as an ACI of MIB group 302 a and sends to NMS 104. As a result, the computation of the incremental checksum is useful in reducing the time taken to compute a checksum of a large number of MIB object instances 204 at periodic intervals of time.

A method for detecting a changed MIB group 302 a using the received ACI is explained in detail in conjunction with FIG. 5, which illustrates a flowchart of a method for detecting a changed MIB group 302 a, in accordance with an embodiment of the present invention. At 502, NMS 104 polls MIB group 302 a. As explained earlier, SNMP agent 202 computes and sends the ACI of MIB group 302 a to NMS 104 in form of SNMP packets. At 504, NMS determines if value of the received ACI is equal to a previous ACI. The previous ACI is the ACI that has been polled in a previous SNMP polling. The previous ACI is persisted at NMS 104 until next polling. The previous ACI and the received ACI are computed for MIB group 302 a by SNMP agent 202. If the received ACI is equal to the previous ACI, it implies that no changes have taken place in MIB object instances 204 since previous polling. This means that network 100 and network device 102 remain at an unchanged operating level. Accordingly, there is no need to poll MIB object instances 204.

However, if the received ACI of MIB group 302 a is not equal to the previous ACI of MIB group 302 a, then, at 506, MIB object instances 204 of MIB group 302 a are polled to detect the changed MIB object instances 204.

A method for detecting whether MIB group 302 a has changed or not has been explained with the help of following exemplary MIB definition:

ifOperStateChgId AggregateChangeIdentifier OBJECTS {  ifOperStatus } STATUS  current DESCRIPTION  “ Aggregate change identifier for all instances of ifOperStatus  available on the network device.” ::= { ifChgId 1 } Computer program source code, object code, instructions, text or other functional information that is executable by a machine may be included in an appendix, tables, figures or in other forms. The copyright owner has no objection to the facsimile reproduction of the specification as filed in the Patent and Trademark Office. Otherwise all copyright rights are reserved. In the above mentioned exemplary MIB definition, ‘ifOperStatus’ is MIB group 302 a and ‘ifOperStateChgId’ is an ACI of MIB group 302 a. MIB group 302 a includes MIB object instances 204.

In accordance with an embodiment of the present invention, if the received ACI is not equal to the previous ACI of the MIB object instance, then, NMS 104 polls the MIB object instances to detect changed MIB object instances. The changed MIB object instances reflect the changes in network device 102 a and network 100.

In an embodiment of the present invention, MIB group 304 a can be a tabular MIB object including a large list of MIB object instances 204. In case, a change is detected in the ACI of MIB group 304 a, NMS 104 has to poll each of MIB object instances 204. The polling of each of MIB object instances 204 results in an increase in SNMP traffic in network 100. Moreover, the time taken by NMS 104 to detect changes in network device 102 a is also increased. In an embodiment of the present invention, MIB object instances 204 are grouped to form MIB groups 302. MIB object instances 204 are grouped to form MIB groups 302 on the basis of a table-compression factor. The table-compression factor is equal to the number of MIB object instances 204 that are grouped to form MIB group 302 a or 302 b. For example, if the table-compression factor is 1:100, then 100 MIB object instances 204 of a table are grouped to form MIB group 302 a. Similarly, next 100 MIB object instances 204 of the table are grouped to form MIB group 302 b. The table-compression factor is defined in the MIB definition. The ACIs of MIB groups 302 a and 302 b can have an object name similar to that of the ACI of the tabular MIB object but should have different indices. An index of MIB group 302 a is equal to a product of the table-compression factor and total number of groups. The total number of groups is obtained by adding one to the number of MIB groups preceding MIB group 302 a. The polling of the tabular MIB object is furthered explained with the help of the following exemplary MIB definition:

   ifOperStateRangeChgId AggregateChangeIdentifier  OBJECTS {   ifOperStatus  }  STATUS  current  DESCRIPTION   “Aggregate change identifier for a set of instances from the start   of the table in lexicographical order of ifOperStatus available on   the network device.”  TABLE-COMPRESSION-FACTOR 1:100 indicates that for every 100 instances from start of the table there will be an instance in the ifOperStateRangeChgId  ::= { ifChgId 1 } Computer program source code, object code, instructions, text or other functional information that is executable by a machine may be included in an appendix, tables, figures or in other forms. The copyright owner has no objection to the facsimile reproduction of the specification as filed in the Patent and Trademark Office. Otherwise all copyright rights are reserved. In the above-mentioned MIB definition, ‘ifOperStatus’ is the tabular MIB object and ‘ifOperStateRangeChgId’ is an ACI of the tabular MIB object.

In accordance with an embodiment of the present invention, MIB group 304 a is hereinafter referred to as the tabular MIB object. The table-compression factor mentioned in the above example is 1:100. As a result, 100 MIB object instances 204 from the beginning of a table of the tabular MIB object can be grouped to form MIB group 302 a. Further, next 100 MIB object instances 204 can be grouped to form MIB group 302 b. The table-compression factor is illustrative only and is not to be construed as the only acceptable table-compression factor. Typically, the determination of the table-compression factor is based on engineering considerations. The object name of the ACIs of MIB groups 302 is similar to that of the ACI of the tabular MIB object but they have different indices. MIB groups 302 are polled by NMS 104. If a change is detected in the ACI of MIB group 302 a, then NMS 104 can poll MIB object instances 204 of MIB group 302 a. The changes in at least one of the changed MIB object instances 204 reflect the changes in network device 102 a and network 100.

In accordance with an embodiment of the present invention, NMS 104 can poll MIB groups 302 a and 302 b together. In response to a poll request for MIB groups 302 a and 302 b, SNMP agent 202 sends an ACI of MIB groups 302 a and 302 b. The ACI of MIB groups 302 a and 302 b is the ACI of MIB object instances 204 of MIB groups 302 a and 302 b. In case, if a change is detected in the ACI of MIB groups 302 a and 302 b, then, NMS 104 polls MIB object instances 204 of MIB groups 302 a and 302 b. 302. The change is detected in an ACI if the received ACI is not equal to the previous ACI. The polling of MIB groups 302 a and 302 b by NMS 104 has been explained with the help of following exemplary MIB definition:

Example: Multiple objects for change identification ifStateChgId AggregateChangeIdentifier  OBJECTS {   ifOperStatus,   ifSpeed  }  STATUS  current  DESCRIPTION   “Aggregate change identifier for all instances of MIB objects   as mentioned in the objects clause.”  ::= { ifChgId 1 } Computer program source code, object code, instructions, text or other functional information that is executable by a machine may be included in an appendix, tables, figures or in other forms. The copyright owner has no objection to the facsimile reproduction of the specification as filed in the Patent and Trademark Office. Otherwise all copyright rights are reserved. In the above-mentioned exemplary MIB definition, ‘ifOperStatus’ is MIB group 302 a and ‘if Speed’ is MIB group 302 b and ‘if StateChgId’ is an ACI of MIB groups 302 a and 302 b. The ACI of MIB groups 302 a and 302 b is equal to the ACI of MIB object instances 204 of MIB groups 302 a and 302 b. MIB groups 302 a and 302 b are polled by NMS 104. NMS 104 receives the ACI of the MIB object instances 204 in response to a poll request. If a change is detected in the ACI of the MIB object instances 204, then, NMS 104 polls MIB object instances 204. The changes in the MIB object instances 204 reflect the changes in network device 102 a and network 100.

In accordance with an embodiment of the present invention, the sensitivity of NMS 104 to changes in network 100 is increased without increasing the traffic in network 100. Sensitivity is defined as the rate at which NMS 104 responds to changes in network 100. Further, sensitivity depends on rate of polling of network devices 102 by NMS 104. For example, if NMS 104 takes 30 minutes to poll each of MIB object instances 204, then NMS 104 can start next polling only after completion of polling of each of MIB object instances 204. As a result, the rate at which the changes are detected in network devices 102 depends on the rate of polling each of MIB object instances 204. When NMS 104 polls MIB groups 302 or 304, the time taken by NMS 104 to detect the changes in network 100 is considerably reduced and thus sensitivity of NMS 104 to changes in network 100 is increased.

In accordance with another embodiment of the present invention, the SNMP polling between NMS 104 and SNMP agent 202 is optimized, as the number of MIB object instances 204 polled is almost proportional to the number of changes in network 100.

In accordance with another embodiment of the present invention, NMS 104 is updated about the changes in network 100 by periodically detecting changes in MIB object instances 204.

In accordance with another embodiment of the present invention, MIB object instances 204 of MIB group 302 a are polled by NMS 104 if a change is detected in MIB group 302 a.

In accordance with an embodiment of the present invention, MIB groups 302 are polled to detect the changed MIB group 302 a.

In accordance with an embodiment of the present invention, only those MIB object instances 204 are allowed to be grouped to form MIB groups 302 and 304 that satisfy certain conditions of grouping, thereby, increasing the efficiency of SNMP polling.

In accordance with an embodiment of the present invention, a multi-level hierarchy of MIB object instances 204 and MIB groups 302 and 304 helps in localizing the changed MIB object instances 204 easily.

In accordance with an embodiment of the present invention, NMS 104 stores the received ACIs for future references.

In accordance with an embodiment of the present invention, the tabular MIB object includes MIB groups 302, wherein MIB groups 302 are formed for easy detection of the changed MIB object instances 204.

In accordance with an embodiment of the present invention, a user can configure MIB groups 302 and 304.

In accordance with an embodiment of the present invention, the ‘dirty information’ can be used for computing an incremental checksum instead of repeatedly computing checksum on MIB groups 302 and 304.

In accordance with an embodiment of the present invention, a method for detecting changes in a network for updating a Network Management Station (NMS), the network comprising the NMS and network devices, each of the network devices comprising a Simple Network Management Protocol (SNMP) agent and Management Information Base (MIB) objects is provided. The method comprising polling an MIB group periodically, the MIB group is formed by grouping MIB object instances; and polling the MIB object instances of the MIB group if a change is detected in an Aggregate Change Identifier (ACI) of the MIB group.

In accordance with another embodiment of the present invention, a method for detecting changes in a network for updating a Network Management Station (NMS), the network comprising the NMS and network devices, each of the network devices comprising a Simple Network Management Protocol (SNMP) agent and Management Information Base (MIB) objects is provided. The method comprising computing an ACI of an MIB group, the MIB group is formed by grouping MIB object instances; and sending the computed ACI to the NMS in response to a request for the MIB group, wherein the request is made by the NMS.

In accordance with an embodiment of the present invention, a system for detecting changes in a network for updating a Network Management Station (NMS), the network comprising the NMS and network devices, each of the network devices comprising a Simple Network Management Protocol (SNMP) agent and Management Information Base (MIB) objects is provided. The system comprising means for polling an MIB group periodically, the MIB group is formed by grouping MIB object instances; and means for polling the MIB object instances of the MIB group if a change is detected in an Aggregate Change Identifier (ACI) of the MIB group.

In accordance with another embodiment of the present invention, a system for detecting changes in a network for updating a Network Management Station (NMS), the network comprising the NMS and network devices, each of the network devices comprising a Simple Network Management Protocol (SNMP) agent and Management Information Base (MIB) objects is provided. The system comprising means for computing an ACI of an MIB group, the MIB group is formed by grouping MIB object instances; and means for sending the computed ACI to the NMS in response to a request for the MIB group, wherein the request is made by the NMS.

An embodiment of the present invention provides a machine-readable medium that includes instructions executable by a computer processor. One or more of these instructions compute an ACI of an MIB group, the MIB group is formed by grouping MIB object instances. Other instructions send the computed ACI to the NMS in response to a request for the MIB group, wherein the request is made by the NMS.

An embodiment of the present invention provides a machine-readable medium that includes instructions executable by a computer processor. One or more of these instructions periodically poll an MIB group, the MIB group is formed by grouping MIB object instances. Other instructions poll the MIB object instances of the MIB group if a change is detected in an Aggregate Change Identifier (ACI) of the MIB group.

Although specific protocols have been used to describe embodiments, other embodiments can use other transmission protocols or standards. Use of the terms ‘peer’, ‘client’, and ‘server’ can include any type of device, operation, or other process. The present invention can operate between any two processes or entities including users, devices, functional systems, or combinations of hardware and software. Peer-to-peer networks and any other networks or systems where the roles of client and server are switched, change dynamically, or are not even present, are within the scope of the invention.

Any suitable programming language can be used to implement the routines of the present invention including C, C++, Java, assembly language, etc. Different programming techniques such as procedural or object oriented can be employed. The routines can execute on a single processing device or multiple processors. Although the steps, operations, or computations may be presented in a specific order, this order may be changed in different embodiments. In some embodiments, multiple steps shown sequentially in this specification can be performed at the same time. The sequence of operations described herein can be interrupted, suspended, or otherwise controlled by another process, such as an operating system, kernel, etc. The routines can operate in an operating system environment or as stand-alone routines occupying all, or a substantial part, of the system processing.

Also in the description herein for embodiments of the present invention, a portion of the disclosure recited in the specification contains material, which is subject to copyright protection. Computer program source code, object code, instructions, text or other functional information that is executable by a machine may be included in an appendix, tables, figures or in other forms. The copyright owner has no objection to the facsimile reproduction of the specification as filed in the Patent and Trademark Office. Otherwise all copyright rights are reserved.

A ‘computer’ for purposes of embodiments of the present invention may include any processor-containing device, such as a mainframe computer, personal computer, laptop, notebook, microcomputer, server, personal data manager or ‘PIM’ (also referred to as a personal information manager), smart cellular or other phone, so-called smart card, set-top box, or any of the like. A ‘computer program’ may include any suitable locally or remotely executable program or sequence of coded instructions, which are to be inserted into a computer, well known to those skilled in the art. Stated more specifically, a computer program includes an organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. A computer program contains a list of ingredients (called variables) and a list of directions (called statements) that tell the computer what to do with the variables. The variables may represent numeric data, text, audio or graphical images. If a computer is employed for presenting media via a suitable directly or indirectly coupled input/output (I/O) device, the computer would have suitable instructions for allowing a user to input or output (e.g., present) program code and/or data information respectively in accordance with the embodiments of the present invention.

A ‘computer readable medium’ for purposes of embodiments of the present invention may be any medium that can contain, store, communicate, propagate, or transport the computer program for use by or in connection with the instruction execution system apparatus, system or device. The computer readable medium can be, by way of example only but not by limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, system, device, propagation medium, or computer memory.

Reference throughout this specification to “one embodiment”, “an embodiment”, or “a specific embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention and not necessarily in all embodiments. Thus, respective appearances of the phrases “in one embodiment”, “in an embodiment”, or “in a specific embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the present invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention.

Further, at least some of the components of an embodiment of the invention may be implemented by using a programmed general-purpose digital computer, by using application specific integrated circuits, programmable logic devices, or field programmable gate arrays, or by using a network of interconnected components and circuits. Connections may be wired, wireless, by modem, and the like.

It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application.

Additionally, any signal arrows in the drawings/Figures should be considered only as exemplary, and not limiting, unless otherwise specifically noted. Combinations of components or steps will also be considered as being noted, where terminology is foreseen as rendering the ability to separate or combine is unclear.

As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

The foregoing description of illustrated embodiments of the present invention, including what is described in the abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention.

Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. As a result, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. 

1. A method comprising: accessing management information base (MIB) object instance update frequency information that reflects a frequency of updates to values of MIB object instances during operation of a network device in a network; selecting, based on at least the accessed MIB object instance update frequency information, a subset of less than all MIB object instances; populating, at the network device, a MIB group with identifiers associated with MIB object instances that are included in the selected subset of less than all MIB object instances; receiving, from a network management system (NMS), a request for information associated with MIB object instances included in the network device; responsive to receiving the request, determining whether changes are made to the MIB object instances for which corresponding identifiers are populated to the MIB group; based on a determination of a change in at least one of the MIB object instances, modifying an existing aggregate change identifier (ACI) for the MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances associated with identifiers included in the MIB group; computing an updated ACI for the MIB group, wherein the updated ACI is an incremental checksum that is computed using the existing ACI that is modified; and sending the updated ACI to the NMS.
 2. The method of claim 1, wherein modifying the ACI for the MIB group further includes marking as invalid the ACI for the MIB group.
 3. The method of claim 1, further comprising: based on a determination that none of the MIB object instances has changed since a previous time at which the existing ACI was computed for the MIB group, sending the existing ACI to the NMS.
 4. The method of claim 1, wherein selecting a subset of less than all MIB object instances further comprises: selecting MIB object instances for which at least one change indicates at least one condition selected from a group including a configuration change of the network device, a behavioral change of the network device and a response of the network device to a change in the network.
 5. The method of claim 1, wherein an ACI is based on at least one parameter selected from a group including a checksum of the MIB group, a timestamp of the MIB group and a combination of a number of MIB object instances in the MIB group and checksum of the MIB group.
 6. The method of claim 1, wherein an ACI has a size in memory that is selected from a group including a 32 byte word and a 64 byte word.
 7. A method comprising: polling a network device in a network, wherein the polling includes sending a request to the network device for information associated with a MIB group, the MIB group including identifiers corresponding to MIB object instances included in the network device that are associated with the MIB group; receiving, from the network device, an ACI that is associated with the MIB group, wherein the ACI is a checksum computed using configuration values of the MIB object instances associated with identifiers included in the MIB group; comparing the received ACI with a cached ACI for the MIB group, wherein the cached ACI is an ACI associated with the MIB group that was received from the network device in response to a previous polling; based on the comparing, determining whether the received ACI is different from the cached ACI, wherein a difference indicates a change in at least one MIB object instance associated with identifiers included in the MIB group; based on determining that the received ACI is different from the cached ACI, polling the network device to determine which MIB object instances associated with identifiers included in the MIB group have changed since the previous polling; and replacing the cached ACI with the received ACI.
 8. A method comprising: generating, at a network device, a plurality of first-level MIB groups; generating a plurality of subsets of MIB object instances, wherein each subset in the plurality of subsets includes a number of MIB object instances that is less than all MIB object instances in the network device; for each MIB group in the plurality of first-level MIB groups, populating the MIB group with identifiers corresponding to MIB object instances that are included in one selected subset in the plurality of subsets, wherein each MIB group in the plurality of first-level MIB groups is associated with a different subset in the plurality of subsets; generating, at the network device, a second-level MIB group, wherein the second-level MIB group includes the plurality of first-level MIB groups; receiving, from an NMS, a request for information associated with MIB object instances included in the network device; responsive to receiving the request, determining, for each first-level MIB group, whether changes are made to the MIB object instances for which corresponding identifiers are included in the first-level MIB group; based on a determination of a change in at least one MIB object instance associated with a particular first-level MIB group, modifying an existing ACI for the particular first-level MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances corresponding to identifiers included in the associated first-level MIB group; computing a first updated ACI for the particular first-level MIB group, wherein the first updated ACI is an incremental checksum that is computed using the existing ACI that is modified; computing a second updated ACI for the second-level MIB group, wherein the second updated ACI is computed based on the first updated ACI for the particular first-level MIB group, and existing ACIs for remaining first-level MIB groups; and sending the second updated ACI to the NMS.
 9. The method of claim 8, the method further comprising: generating, at the network device, a plurality of second-level MIB groups, wherein each second-level MIB group in the plurality of second-level MIB groups includes a subset of first-level MIB groups such that the subset of first-level MIB groups included in a second-level MIB group is different from the subsets of first-level MIB groups included in other second-level MIB groups; and generating, at the network device, a third-level MIB group, wherein the third-level MIB group includes the plurality of second-level MIB groups.
 10. The method of claim 8, wherein modifying the existing ACI for the particular first-level MIB group further includes marking as invalid the ACI for the particular first-level MIB group.
 11. The method of claim 8, further comprising: based on a determination that none of the MIB object instances has changed since a previous time at which existing ACIs were computed for the first-level MIB groups, sending the existing ACI for the second-level MIB group to the NMS.
 12. The method of claim 8, wherein generating a plurality of subsets of MIB object instances further comprises: for each subset in the plurality of subsets, selecting MIB object instances based on a table compression factor, the table compression factor being equal to a number of MIB object instances that are grouped to form a first-level MIB group.
 13. A method comprising: polling a network device in a network, wherein the polling includes sending a request to the network device for information associated with MIB object instances included in the network device, and wherein the MIB object instances are grouped into a plurality of first-level MIB groups, a first-level MIB group including identifiers corresponding to MIB object instances that are associated with the respective first-level MIB group, and wherein the plurality of first-level MIB groups are grouped into a second-level MIB group; receiving, from the network device, a second ACI that is associated with the second-level MIB group, wherein the second ACI is based on ACIs for the plurality of first-level MIB groups, an ACI for a first-level MIB group being a checksum computed using configuration values of the MIB object instances associated with identifiers included in the corresponding first-level MIB group; comparing the received second ACI with a cached second ACI for the second-level MIB group, wherein the cached second ACI is an ACI associated with the second-level MIB group that was received from the network device in response to a previous polling; based on the comparing, determining whether the received second ACI is different from the cached second ACI, wherein a difference indicates a change in at least one ACI associated with a first-level MIB group; based on determining that the received second ACI is different from the cached second ACI, polling the network device to determine which ACIs associated with first-level MIB groups have changed since the previous polling; and replacing the cached second ACI with the received second ACI.
 14. The method of claim 13, the method further comprising: receiving, from the network device, a plurality of first ACIs that are associated with the first-level MIB groups; for each received first ACI: comparing the first ACI with a cached first ACI for the respective first-level MIB group, wherein the cached first ACI is an ACI associated with the respective first-level MIB group that was received from the network device in response to a previous polling; based on the comparing, determining whether the received first ACI is different from the cached first ACI, wherein a difference indicates a change in at least one MIB object instance associated with identifiers included in the respective first-level MIB group; based on determining that the received first ACI is different from the cached first ACI, polling the network device to determine which MIB object instances associated with identifiers included in the respective first-level MIB group have changed since the previous polling; and replacing the cached first ACI with the received first ACI.
 15. A system comprising: a first network device including a first processor and a plurality of first instructions stored in a non-transitory machine-readable first medium for execution by the first processor, the plurality of first instructions when executed cause the first processor to perform operations including: accessing management information base (MIB) object instance update frequency information that reflects a frequency of updates to values of MIB object instances during operation of the first network device in a network; selecting, based on at least the accessed MIB object instance update frequency information, a subset of less than all MIB object instances; populating, at the network device, a MIB group with identifiers associated with MIB object instances that are included in the selected subset of less than all MIB object instances; receiving, from a second network device in the network, a request for information associated with MIB object instances included in the first network device; responsive to receiving the request, determining whether changes are made to the MIB object instances for which corresponding identifiers are populated to the MIB group; based on a determination of a change in at least one of the MIB object instances, modifying an existing aggregate change identifier (ACI) for the MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances associated with identifiers included in the MIB group; computing an updated ACI for the MIB group, wherein the updated ACI is an incremental checksum that is computed using the existing ACI that is modified; and sending the updated ACI to the second network device; and the second network device including a second processor and a plurality of second instructions stored in a non-transitory machine-readable second medium for execution by the second processor, the plurality of second instructions when executed cause the second processor to perform operations including: polling the first network device, wherein the polling includes sending a request to the network device for information associated with the MIB group including identifiers corresponding to MIB object instances included in the first network device that are associated with the MIB group; receiving, from the first network device, an ACI that is associated with the MIB group; comparing the received ACI with a cached ACI for the MIB group, wherein the cached ACI is an ACI associated with the MIB group that was received from the first network device in response to a previous polling; based on the comparing, determining whether the received ACI is different from the cached ACI, wherein a difference indicates a change in at least one MIB object instance associated with identifiers included in the MIB group; based on determining that the received ACI is different from the cached ACI, polling the first network device to determine which MIB object instances associated with identifiers included in the MIB group have changed since the last polling; and replacing the cached ACI with the received ACI.
 16. A non-transitory machine-readable medium including a plurality of instructions for execution by at least one processor, the plurality of instructions when executed cause the at least one processor to perform operations including: accessing management information base (MIB) object instance update frequency information that reflects a frequency of updates to values of MIB object instances during operation of a network device in a network; selecting, based on at least the accessed MIB object instance update frequency information, a subset of less than all MIB object instances; populating, at the network device, a MIB group with identifiers associated with MIB object instances that are included in the selected subset of less than all MIB object instances; receiving, from a network management system (NMS), a request for information associated with MIB object instances included in the network device; responsive to receiving the request, determining whether changes are made to the MIB object instances for which corresponding identifiers are populated to the MIB group; based on a determination of a change in at least one of the MIB object instances, modifying an existing aggregate change identifier (ACI) for the MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances associated with identifiers included in the MIB group; computing an updated ACI for the MIB group, wherein the updated ACI is an incremental checksum that is computed using the existing ACI that is modified; and sending the updated ACI to the NMS.
 17. A non-transitory machine-readable medium including a plurality of instructions for execution by at least one processor, the plurality of instructions when executed cause the at least one processor to perform operations including: polling a network device in a network, wherein the polling includes sending a request to the network device for information associated with a MIB group, the MIB group including identifiers corresponding to MIB object instances included in the network device that are associated with the MIB group; receiving, from the network device, an ACI that is associated with the MIB group, wherein the ACI is a checksum computed using configuration values of the MIB object instances associated with identifiers included in the MIB group; comparing the received ACI with a cached ACI for the MIB group, wherein the cached ACI is an ACI associated with the MIB group that was received from the network device in response to a previous polling; based on the comparing, determining whether the received ACI is different from the cached ACI, wherein a difference indicates a change in at least one MIB object instance associated with identifiers included in the MIB group; based on determining that the received ACI is different from the cached ACI, polling the network device to determine which MIB object instances associated with identifiers included in the MIB group have changed since the previous polling; and replacing the cached ACI with the received ACI.
 18. A system comprising: a first network device including a first processor and a plurality of first instructions stored in a non-transitory machine-readable first medium for execution by the first processor, the plurality of first instructions when executed cause the first processor to perform operations including: generating, at the first network device, a plurality of first-level MIB groups; generating a plurality of subsets of MIB object instances, wherein each subset in the plurality of subsets includes a number of MIB object instances that is less than all MIB object instances in the first network device; for each MIB group in the plurality of first-level MIB groups, populating the MIB group with identifiers corresponding to MIB object instances that are included in one selected subset in the plurality of subsets, wherein each MIB group in the plurality of first-level MIB groups is associated with a different subset in the plurality of subsets; generating, at the first network device, a second-level MIB group, wherein the second-level MIB group includes the plurality of first-level MIB groups; receiving, from a second network device, a request for information associated with MIB object instances included in the first network device; responsive to receiving the request, determining, for each first-level MIB group, whether changes are made to the MIB object instances for which corresponding identifiers are included in the first-level MIB group; based on a determination of a change in at least one MIB object instance associated with a particular first-level MIB group, modifying an existing ACI for the particular first-level MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances corresponding to identifiers included in the associated first-level MIB group; computing a first updated ACI for the particular first-level MIB group, wherein the first updated ACI is an incremental checksum that is computed using the existing ACI that is modified; computing a second updated ACI for the second-level MIB group, wherein the second updated ACI is computed based on the first updated ACI for the particular first-level MIB group, and existing ACIs for remaining first-level MIB groups; sending the second updated ACI to the second network device; and the second network device including a second processor and a plurality of second instructions stored in a non-transitory machine-readable second medium for execution by the second processor, the plurality of second instructions when executed cause the second processor to perform operations including: polling the first network device, wherein the polling includes sending a request to the first network device for information associated with MIB object instances included in the network device; receiving, from the first network device, a second ACI that is associated with the second-level MIB group; comparing the received second ACI with a cached second ACI for the second-level MIB group, wherein the cached second ACI is an ACI associated with the second-level MIB group that was received from the first network device in response to a previous polling; based on the comparing, determining whether the received second ACI is different from the cached second ACI, wherein a difference indicates a change in at least one ACI associated with a first-level MIB group; based on determining that the received second ACI is different from the cached second ACI, polling the first network device to determine which ACIs associated with first-level MIB groups have changed since the last polling; and replacing the cached second ACI with the received second ACI.
 19. A non-transitory machine-readable medium including a plurality of instructions for execution by at least one processor, the plurality of instructions when executed cause the at least one processor to perform operations including: generating, at a network device, a plurality of first-level MIB groups; generating a plurality of subsets of MIB object instances, wherein each subset in the plurality of subsets includes a number of MIB object instances that is less than all MIB object instances in the network device; for each MIB group in the plurality of first-level MIB groups, populating the MIB group with identifiers corresponding to MIB object instances that are included in one selected subset in the plurality of subsets, wherein each MIB group in the plurality of first-level MIB groups is associated with a different subset in the plurality of subsets; generating, at the network device, a second-level MIB group, wherein the second-level MIB group includes the plurality of first-level MIB groups; receiving, from an NMS, a request for information associated with MIB object instances included in the network device; responsive to receiving the request, determining, for each first-level MIB group, whether changes are made to the MIB object instances for which corresponding identifiers are included in the first-level MIB group; based on a determination of a change in at least one MIB object instance associated with a particular first-level MIB group, modifying an existing ACI for the particular first-level MIB group, wherein an ACI is a checksum computed using configuration values of the MIB object instances corresponding to identifiers included in the associated first-level MIB group; computing a first updated ACI for the particular first-level MIB group, wherein the first updated ACI is an incremental checksum that is computed using the existing ACI that is modified; computing a second updated ACI for the second-level MIB group, wherein the second updated ACI is computed based on the first updated ACI for the particular first-level MIB group, and existing ACIs for remaining first-level MIB groups; and sending the second updated ACI to the NMS.
 20. A non-transitory machine-readable medium including a plurality of instructions for execution by at least one processor, the plurality of instructions when executed cause the at least one processor to perform operations including: polling a network device in a network, wherein the polling includes sending a request to the network device for information associated with MIB object instances included in the network device, and wherein the MIB object instances are grouped into a plurality of first-level MIB groups, a first-level MIB group including identifiers corresponding to MIB object instances that are associated with the respective first-level MIB group, and wherein the plurality of first-level MIB groups are grouped into a second-level MIB group; receiving, from the network device, a second ACI that is associated with the second-level MIB group, wherein the second ACI is based on ACIs for the plurality of first-level MIB groups, an ACI for a first-level MIB group being a checksum computed using configuration values of the MIB object instances associated with identifiers included in the corresponding first-level MIB group; comparing the received second ACI with a cached second ACI for the second-level MIB group, wherein the cached second ACI is an ACI associated with the second-level MIB group that was received from the network device in response to a previous polling; based on the comparing, determining whether the received second ACI is different from the cached second ACI, wherein a difference indicates a change in at least one ACI associated with a first-level MIB group; based on determining that the received second ACI is different from the cached second ACI, polling the network device to determine which ACIs associated with first-level MIB groups have changed since the previous polling; and replacing the cached second ACI with the received second ACI. 